Mariner 4 was the next successful spacecraft in the Mariner program after Mariner 2's encounter with Venus.

The project targeted Mars with two spacecraft. Mariner 3 was launched on November 5, 1964, but the shroud encasing the spacecraft atop its rocket failed to open properly and spacecraft did not get to Mars. Three weeks later, on November 28, 1964, Mariner 4 was launched successfully from Cape Kennedy on an eight-month voyage to the red planet. The spacecraft flew past Mars on July 14, 1965, collecting the first close-up photographs of another planet. The pictures, played back from a small tape recorder over a long period, showed lunar-type impact craters, some of them touched with frost in the chill Martian evening. The Mariner 4 spacecraft, expected to survive something more than the eight months to Mars encounter, actually lasted about three years in solar orbit, continuing long-term studies of the solar wind environment and making coordinated measurements with Mariner 5, a sister ship launched to Venus in 1967.